Answer:
31. marry
32. fall
33. adopt
34. On
35. nuclear
Step-by-step explanation:
31. Marry is the most common verb for getting married.
32. fall is the most appropriate verb to describe how few families now fit into the traditional two-parent family category.
33. adopt is the most appropriate verb to describe how unmarried couples may take in foster children or adopt children.
34. On is the most appropriate preposition to use in this sentence because it indicates the time period in which some people believe similar events happen again and again in history.
35. nuclear is the most appropriate adjective to describe the traditional two-parent family of the past.